1. Field of the Invention
The invention relates to an abnormality detection apparatus and an abnormality detection method for a Rankine cycle system in which waste heat produced by an internal combustion engine is recovered via vapor.
2. Description of Related Art
A waste heat recovery apparatus that recovers waste heat produced in connection with the driving of an internal combustion engine by using the Rankine cycle is known. In a waste heat recovery apparatus of this kind, a water-cooled cooling system of an internal combustion engine is constructed so as to have a sealed structure, and an expander (turbine) is driven by using a cooling medium (vapor) vaporized by waste heat of the internal combustion engine, and thermal energy that the vapor has is recovered by converting it into mechanical power or electric energy. For example, a waste heat recovery apparatus described in Japanese Patent Application Publication No. 2008-169760 (JP-A-2008-169760) converts thermal energy into electric energy by supplying the coolant from the engine to a superheater via a gas-liquid separator so that the coolant vaporizes, and then actuating the expander through the use of the generated vapor.
Besides, apparatuses that determine the presence or absence of failure of such a waste heat recovery apparatus have been disclosed as mentioned below. For example, a waste heat recovery apparatus described in Japanese Patent Application Publication No. 2008-169731 (JP-A-2008-169731) determines whether there is leakage of vapor in a supply passageway to a turbine in a Rankine cycle system by calculating from the engine rotation speed a predicted amount of recovery work (amount of electricity generation) of the expander and then comparing the multiplication product of the predicted amount of recovery work and a correction coefficient with the absolute value of an actually measured amount of recovery work (amount of electricity generation) of the expander. A waste heat recovery apparatus described in Japanese Patent Application Publication No. 2010-174848 (JP-A-2010-174848) determines whether a cooling medium pump has failure by monitoring the pressure in a circuit of the Rankine cycle by using a cooling medium pressure sensor that is provided in a flow path between a cooling medium pump and an evaporator. A heat cycle apparatus described in Japanese Patent Application Publication No. 2006-17108 (JP-A-2006-17108) determines whether the Rankine cycle has abnormality by comparing a difference value between an upstream pressure value and a downstream pressure value of a liquid pump with a predetermined pressure value. Japanese Patent Application Publication No. 59-43910 (JP-A-59-43910) describes that, in the Rankine cycle, abnormality of a turbine is detected on the basis of changes in the output of an electricity generator. Japanese Patent Application Publication No. 2006-170185 (JP-A-2006-170185) describes that, in the Rankine cycle, a control abnormality of an electricity generator is detected on the basis of the rotation speed of an electricity generator that is integrated with an expander. Japanese Patent Application Publication No. 2008-255923 (JP-A-2008-255923) describes that, in the Rankine cycle, leakage of a working fluid is detected. Furthermore, Japanese Patent Application Publication No. 61-152920 (JP-A-61-152920) discloses an ebullient cooling apparatus for an internal combustion engine which detects an abnormality, such as the clogging of a condenser, or the like, if an output value of a temperature sensor provided in a reservoir tank is greater than or equal to a reference value.
By the way, in a Rankine cycle system that recovers waste heat of an internal combustion engine, waste heat from the internal combustion engine cannot be recovered if the cooling medium or vapor that is a working fluid does not circulate normally in the Rankine cycle system. When the working fluid does not circulate normally in the Rankine cycle system, various causes are conceivable, including a failure of a cooling system of the internal combustion engine, a failure of an electromagnetic valve or a water pump disposed in a passageway through which the working fluid circulates, a leak of the working fluid between passageways, etc. Therefore, in order to specifically determine the cause of the working fluid failing to circulate normally in the Rankine cycle system, it cannot be said to be sufficient to merely perform a determination regarding a single cause. That is, it is necessary to synthetically perform determination regarding events that can be causes of the failure in the normal circulation of the working fluid in the Rankine cycle. However, although there have been disclosed apparatuses that perform determination regarding individual causes of the failure in the normal circulation of the working fluid in the Rankine cycle system, a construction that synthetically performs determination regarding such causes has not been disclosed. Hence, the Rankine cycle system still has room for betterment.